When acquiring an X-ray image, an object to be examined, e.g. a patient, is arranged between an X-ray source or generating device, e.g. an X-ray tube, and an X-ray detection system. Radiation emanating from the X-ray source is penetrating the object to be examined, subsequently arriving at the X-ray detection system. Conventional computed tomography (CT) measures the linear attenuation coefficient of objects.
In phase-contrast imaging, or phase contrast computed tomography, at least partly spatially coherent or quasi coherent radiation in a line pattern is employed. Coherent or quasi coherent X-rays penetrating the object may allow for subsequent retrieval of phase information. X-ray phase-contrast imaging is described, for example, in Weitkamp T., Diaz A., David C. et al.: “X-ray phase imaging with a grating interferometer”; Optics Express 6296, 8, Aug. 2005, Vol. 13, No. 16. Grating based phase contrast imaging systems further provide dark field images which are indicative for the small angle scattering power of the sample. This aspect is detailed in M. Bech, O. Bunk, T. Donath et al.: “Quantitative x-ray dark-field computed tomography”; Phys. Med. Biol. 55 (2010) 5529-5539.
An increase in the fan angle of an X-ray beam may lead to a reduced structure visibility. In particular in medical application, which requires large fan angles of X-ray beam due to object size, this can result in a significant loss of structure visibility.